The present invention relates to a method and apparatus for forming a rod-like filler which consists of fibrous material, and more particularly to improvements in a method and apparatus for converting a continuous tobacco stream into a continuous rod-like tobacco filler, e.g., a filler which can be draped into cigarette paper or other suitable wrapping material and severed to yield a succession of discrete cigarettes, cigars or cigarillos.
It is known to form a rod-like filler by resorting to a distributor which showers, propels or otherwise advances tobacco or other fibrous material against one side of an elongated stream forming conveyor and by thereupon removing the surplus from an uneven surface of the resulting tobacco stream. The surplus is removed by one or more trimming or equalizing devices which are normally adjacent to that side or surface of the stream which faces away from the conveyor. The term "fibrous material" is intended to denote natural and reconstituted tobacco, substitutes for tobacco, tobacco shreds, fragments of tobacco ribs, tobacco leaves of the type used in the wrappers of cigars or cigarillos, fibrous filter material and analogous substances. For the sake of simplicity, the invention will be described with reference to continuous bodies (streams and fillers or filler rods) which are composed (either primarily or entirely) of tobacco shreds. It is to be understood, however, that the improved method and apparatus can be utilized with equal advantage for the making of fillers or filler rods which consist of other types or sizes of material or reconstituted tobacco, substitutes for tobacco as well as fibrous filter material.
A satisfactory cigarette maker should be capable of producing discrete cigarettes wherein the density of the fillers is constant except, of course, if the cigarette maker is designed to produce cigarettes with dense ends. Constant density is desirable for a number of reasons including savings in tobacco and absence of excessive deviation of the weight of cigarettes from a predetermined optimum weight. This renders it necessary to subject the tobacco stream to at least one trimming or equalizing action because presently known distributors are incapable of feeding tobacco particles at the rate which is necessary to insure the conversion of particles into a tobacco stream of constant density and constant cross-sectional area. Therefore, the distributor of a cigarette maker invariably feeds tobacco particles in such quantities that the stream contains a surplus of tobacco, and such surplus is removed by the trimming device or devices. The trimming device or devices are adjustable, preferably in response to signals furnished by a detector which monitors the density of the stream ahead of the trimming station. As a rule, the trimming device or devices are movable at right angles to the direction of movement of the stream. If the aforementioned conveyor includes or constitutes an elongated channel, the trimming device or devices are placed adjacent to that side of the stream which faces away from the bottom wall of the channel. The removed surplus of tobacco is normally returned into the magazine of the distributor.
In order to form a satisfactory filler, the distributor of a cigarette making machine must deliver tobacco at a rate which invariably suffices to form a tobacco stream wherein each and every increment contains a surplus of tobacco particles. In other words, at least the first trimming or equalizing device must remove a surplus from each and every increment of the stream. On the other hand, the quantity of surplus should be held to a minimum because the removal of surplus invariably involves undesirable comminution of particles. Comminuted particles (e.g., relatively short tobacco shreds) cannot be processed with the same degree of predictability as longer or larger particles and, furthermore, the filling effect of shorter particles is much less satisfactory than that of longer shreds. It has been found that accumulations of shorter shreds in certain portions of the stream adversely affect the quality of the corresponding portion of the filler.
U.S. Pat. No. 3,132,650 to Richter proposes to change the rate of tobacco delivery by the distributor simultaneously with changes in the position of trimming device as a function of changes in the quantity of surplus tobacco. A drawback of the patented apparatus is that it does not embody any means for accurately determining the quantity of surplus.
U.S. Pat. No. 3,338,247 to Labbe discloses an apparatus wherein the surplus is admitted into a separate path in which the surplus is equalized and measured. The results of measurements are used to regulate the operation of the distributor. Such apparatus also exhibit a number of drawbacks, especially that they do not take into consideration the fact that fluctuations in quantity of tobacco forming the stream depend on a number of factors including the rate of feed by the distributor as well as the quality of tobacco, the configuration of tobacco particles, the condition of tobacco and additional factors which influence the conversion of tobacco particles into a stream (such additional factors include the force of air streams which are used to attract tobacco particles to the stream forming conveyor). Since such factors are not predictable (i.e., their effect upon the quantity of tobacco in the stream arises at irregular intervals), the patented apparatus is incapable of accurately determining the rate at which the distributor should feed tobacco particles in order to reduce the surplus which must be removed by the trimming device or devices.
None of the presently known apparatus take into consideration the geometric shape and/or the exact dimensions of the stream which must be trimmed in order to be converted into an equalized stream.